This invention relates to image projection and television viewing systems. More particularly, this invention relates to a method and apparatus for enabling a centrally located video image to be viewed substantially simultaneously by an audience surrounding the image through a 360.degree. span.
The general problem in the display of a picture print, a television image or a projection onto a screen is that the picture is best viewed when the viewer's line of sight is precisely normal to the plane of the picture. This ideal condition is difficult to realize when several people wish to view the picture simultaneously from varied locations.
One solution to this problem is to simply mount the picture on a rotating pedestal which will slowly rotate over 360.degree., permitting several people surrounding the pedestal to eventually view the picture in a line of sight normal to the plane of the picture. Such systems are often used in advertising displays within large areas such as railroad stations and the like. A problem with such an arrangement is that the rotation of the picture must be relatively slow in order to permit the various viewers to have an opportunity to study the picture. Such a slow rotation means that essentially only a few people at a time are viewing the picture while others out of the line of sight must wait until the picture comes into view.
There are many instances in which several people may wish to view a picture or displayed data simultaneously and continuously so that they can all carry on a meaningful discussion concerning the displayed information. For example, during business meetings a group of executives typically sit around a conference table, an arrangement which does not readily enable information presented on the table to be displayed to all in attendance. A great benefit would be realized if a means centrally located on the table were available which would permit everyone present to examine a picture or projected data substantially simultaneously. For example, the necessity of passing among the members of the group pictures to be successively viewed would be avoided. In addition, the ability to display data through a 360.degree. range would prevent members from looking at a series of pictures out of order, a potential problem if duplicate sets of pictures were to be provided to each individual member.
Another drawback associated with conventional display systems is that special consideration must be given to the positioning of the display within its environment because, typically, conventional display systems, such as a television, cannot be viewed from the rear or extreme sides. Thus, the area within which a viewing audience can be accommodated is limited to locations with suitable sight lines. As a result, use of the space available around the display system is often limited by the presence of blind spots. Moreover, the positioning of furniture within a room can disadvantageously be dictated by a need to provide clear sight lines to a television or the like.
In an attempt to overcome the viewing limitations associated with conventional displays, 360.degree. viewing systems have been developed, examples of which are shown in U.S. Pat. Nos. 3,976,837; 4,901,140; 4,943,851; and 4,979,026, the contents of which are incorporated herein by reference. More particularly, U.S. Pat. No. 4,943,851 disclosed a viewing system for presenting a projected image upon a rear projection screen that is rotated extremely rapidly about a vertical axis which exactly bisects the picture in the vertical plane. The rotational rate of the projection screen is such that an entire audience, regardless of their position about the viewing system, can view the projected image simultaneously. The viewing system features an optical system which rotates with respect to a cathode ray tube about the vertical axis in synchronization with the rotation of the projection screen. A liquid crystal display (LCD) screen is utilized to define a viewing window which is continuously redefined at sequential intervals to remain continually aligned with the projection screen. U.S. Pat. No. 4,901,140 discloses a viewing system that presents a real image in space that itself is rotated extremely rapidly so that an entire audience can view the same image substantially simultaneously and continuously. In this case, a black and white image projected from a cathode ray tube is projected through a parabolic mirror arrangement to provide the real image in space. An LCD screen is utilized to define a filtered viewing window which is continuously redefined at sequential intervals to remain continually aligned with the rotating real image in space. The LCD screen includes normally opaque red, green and blue filter panels which operate to give color to the real image in space. U.S. Pat. No. 4,979,026 discloses the use of a rotatable polarized screen and a separate, stationary polarized screen which cooperate to define a viewing window which remains continually aligned with the rotating real image in space.
Although such prior 360.degree. viewing systems provided significant advancements over the prior art, additional features have been considered desirable in order to provide a more commercially acceptable product. For example, such prior systems have suffered from a visually perceptible blur at the edge of the projected image as it rotates past the viewer's line of sight. It has been found that such horizontal blurring of the image may be reduced by providing a slit in front of the projection screen, which rotates together with the screen. While horizontal image scanning may be accomplished watching the screen through the slit, however, most of the light from the rotating screen is lost on the inside wall of the rotating drum. Only a very small fraction of the projected image goes through the slit to reach the eye of the observer. The drawback of such an approach lies primarily in the reduction of the brightness of the projected image. In this regard, the apparent screen brightness is a function of the time integral of the stationary screen brightness and the visibility function, defined by the slit width. In other words, the apparent brightness of the rotational screen is 50 to 100 times less than the brightness of a stationary screen.
Accordingly, there exists a need for a visual display system that enables an entire audience to view a video image simultaneously regardless of an individual's location around the display system, and which can minimize, to the extent possible, visible blur at the edges of the projected video image. Additionally, an improved 360.degree. viewing system is needed which utilizes a stationary projector and means for rotating the image produced by the projector in order to follow a rotating rear projection screen. The present invention fulfills these needs and provides other related advantages.